Pinocytotic vesicles in alveolar capillary endothelial cells and alveolar type I cells are thought to provide a "shuttle" for the transfer of macromolecules across the alveolar-capillary membrane. The overall objective of this proposal is to perform experiments which will provide insight into factors regulating the number and location of these vesicles. I anticipate that these experiments will generate information relevant to our understanding of macromolecule transport and fluid flow in the lung; this will have relevance to our understanding of pulmonary edema and may provide insights into therapeutic approaches. I expect to achieve this objective using electron microscopic techniques, perfusion fixation of the lung and morphometry.